Compton spectroscopy of hydrogen storage material LiAlH4: Experiment and DFT strategies

Abstract

Electronic structure and momentum densities of three possible phases (α, β and γ) of hydrogen storage material, LiAlH4, are reported using the linear combination of atomic orbitals (LCAO) scheme within the density functional theory (DFT). Energy bands and density of states computed using generalised gradient approximation and hybrid (Hartree-Fock + DFT) potentials show that the studied phases of LiAlH4 possess wide band gaps ranging from 3.59 to 6.64 eV. The experimental Compton profile (CP) of the most stable α-phase was measured using 100 mCi 241Am γ-ray Compton spectrometer. The experimental CP is used to validate the applicability of exchange and correlation energies by comparing it with theoretical CPs deduced using various exchange and correlation potentials. The B3LYP hybrid functional-based CP is found to be in good agreement with the present experimental Compton data. Based on Mulliken's population and valence electron charge density, the trend of ionicity is found in the descending order as γ-phase > α-phase > β-phase. Moreover, the modified Becke-Johnson (mBJ) scheme of the full potential linearized augmented plane wave (FP-LAPW) method is also used to compute the electronic and optical response of LiAlH4, which show its use as absorptive material for ultraviolet radiations. The bonding nature of the Al-H bond and Li+-[AlH4]¯ is also presented using the electron localization function.